In manufacturing lenses and particularly those lenses for use with eyeglasses, it has been desirable to have a number of characteristics, including tinting, multifocal lenses, hard coating, polaroid, photochromatic, safety, and ease of manufacture. Although there are processes presently existing for achieving each of these characteristics, they all have certain deficiencies which have hampered their broad use, particularly with plastic lenses.
For example, when attempting to tint plastic lenses by dipping them into a bath of dye, maintaining a consistent tint has been a difficult problem. Often the dye, because it will be absorbed entirely throughout the lens, will produce a gradient throughout the lens where some portions of the lens are darker than others. This is typically unacceptable to the consumer. If the dye is placed on the surface of the lens, on the other hand, it can easily be scratched or worn, creating an unsightly appearance for the eyeglasses. In multifocal lenses, there are often ledges and other protrusions which are unsightly and unappealing to the consumer. There have been attempts to blend these multifocal lenses to avoid the ledges and other lines defining the multifocal lenses, but these have been relatively expensive processes and some cases, prohibitive.
The invention described herein has overcome many of the deficiencies of the prior art noted above. For example, a tinting process has been developed which maintains consistency throughout a given cross-sectional area and avoids the gradients which have characterized other processes in tinting lenses. To accomplish this feature, a wafer of previously cured, solidified plastic material is tinted to the desired color. This wafer is then used in a mold with a monomer which will be polymerized to eventually form the lens with the tinted wafer formed integrately therewith.
More specifically, when a front mold form is utilized with a surrounding gasket, a portion of a liquid molding material is placed in this portion of the mold form. Subsequently, the tinted wafer is placed in contiguous relationship with the liquid molding material. A rear mold form is then fixed in the gasket spaced from the wafer to form a cavity therein for receiving plastic molding material. Liquid plastic molding material is then delivered into this cavity to completely fill all the voids in the mold.
The mold is then subjected to oven-curing process for solidifying the plastic molding material about the wafer and to cause intermolecular bonding between the molding material and the wafer. After the molding process has been completed, the mold is removed from the oven and the molded lens withdrawn from the mold in a form which is ready after some edge processing for use with eyeglasses. With this process, the tint is constrained generally in the vicinity of the wafer.
In another embodiment of the invention, the tinted wafer forms part of the first mold form of a mold which can be removed from the mold and ultimately form part of the lens as molded. In this instance, this mold form is tinted by dipping into the bath of dye similar to that discussed above. It is then fixed into a portion of the mold with a second mold form being spaced therefrom to form a cavity between the two mold forms. The plastic molding material is then delivered into the mold cavity until it completely fills all the voids therein without any intervening wafer. The mold is then subjected to oven-curing process to solidify the plastic molding material and again to cause the molecular bonding between the molding material and first mold form. After curing, the mold is withdrawn and the lens formed separated from the mold with the first mold form being bonded to the polymerized plastic material. In other words, a portion of the mold is consumed in the molding process and forms part of the formed lens. Prior to this step the front portion of the wafer, which will ultimately be a portion of the lens, can be hard-coated to protect the tint in the remaining portion of the lens. In the embodiment discussed below when the mold form becomes part of the article, it is also referred to as a "preform".
Multifocal lenses can be produced using a similar process to that discussed above. The wafer can be initially formed with a ledge which is part of a segment having a different power than the remaining portion of the wafer. This wafer, when used as an intermediate step in the molding process as discussed above, will have a different material with a different index of refraction than the liquid plastic that will ultimately form part of the lens when cured.
The wafer with the bifocal or multifocal segments will be inserted into the molding process after an initial amount of liquid molding material has been placed into the mold as discussed above. The remaining steps are similar to those of the tinting process.
Where the wafer actually forms the first mold form, the bifocal, or multifocal segment is preferably on the rear surface of the first mold to create a more pleasing and unobtrusive appearance to the consumer. In this case, the wafer will be preformed with the segment having the desired bifocal power. The wafer would then be included with the mold and filled and cured as described above.
Another feature of the invention is to place the segment forming the additional bifocal power on the exterior surface of the lens is ultimately molded. With this feature, a segment mold is secured to the surface of the plastic lens to form with a cavity which corresponds to configuration of the bifocal or multifocal power segment. After having been clamped into position, the mold is filled with liquid molding material and cured as described above. With this feature, the bifocal segment can be placed at any position desired by the doctor to insure that it is in the correct position with regard to the user and not limited to fixed positions of any preforms.
The above has been a brief discussion of certain features of the invention. Other features and advantages of the invention will be appreciated from the detailed discussion of the preferred embodiment below.